ENZYMES Flashcards
Catalyst that speeds up chemical reactions in our cells by lowering the energy required for the reaction. Not consumed in the reaction, just help in speeding up
They are extremely effective, up to 1020 times faster
Specific; react on certain substrates or substances
Most are globular and most effective known catalyst
Enzymes
1,500- 3,000 different enzymes
Since they are proteins, they could undergo denaturation
Classified base on function rather than structure
Almost every reaction in the cell require its own specific enzyme; specific enzyme reacts with specific substrate
Substance that lowers the activation energy of a reaction without being changed itself
Catalyst
Hydrolysis of protein in our diet, found in GI tract: trypsin or pepsin
Carbonic anhydrase in blood
35M reactants in a minute
Enzyme Structure:
An enzyme composed of only one protein
Simple Enzyme
Enzyme Structure:
An enzyme that has a non protein part in addition to protein part
Conjugated Enzyme
Types of Conjugated Enzymes: protein part; lacks the cofactor Catalytically inactive and incomplete Needs a cofactor for it to react or activate on a certain substrate or substance Apoenzyme + cofactor = activated
Apoenzyme
Types of Conjugated Enzymes:
non-protein part
Small organic molecules/ coenzyme or inorganic ions (metal ion; ZN, Mg, Mn, Fe)
Important for the chemically reactive enzymes; makes sure Apoenzyme will be activated
Bind tightly or loosely with the apoenzyme
Derived from dietary minerals
Cofactor
Types of Conjugated Enzymes:
biochemical active conjugated enzyme
Apoenzyme + cofactor = activated enzyme
Once removed from the apoenzyme, it will go back to its original structure
Holoenzyme
Types of Conjugated Enzymes:
co-substrate
Organic molecule co-factors
Derived from dietary vitamins
Coenzyme
Nomenclature and Classification of Enzymes:
Sucrase – reacts sucrose
Lipase - reacts lipid
Identifies a reacting substance
Nomenclature and Classification of Enzymes:
type of reaction catalyzed by an enzyme
Oxidase – catalyzes oxidation
Hydrolase – catalyzes hydrolysis
Describes function of enzyme
6 Classification and Names of Enzymes:
Oxidation-reduction reactions (Redox)
Requires coenzyme
Ex: lactate dehydrogenase (LDH; removes H from lactic acid)
Oxidoreductase
Oxidases
Reductases
Dehydrogenases: removes H
6 Classification and Names of Enzymes:
Transfer a functional group from one molecule to another
Ex: SGOT/AST, SGPT/ALT (transaminases)
Phosphate from ATP —> ADP(kinase; phosphate to substrate)
Transferase
Transaminases: amino group
Kinases: phosphate group from ATP, creatine kinase (CK)
6 Classification and Names of Enzymes:
Hydrolysis reactions: addition of H2O (water)
-Breaks the bond, Reacts when forming a bond or linkage
-Central to the process of digestion
-Reacts with macro/ bio organic molecule
Hydrolase
Proteases: peptide Lipases: ester linkage Carbohydrases: glycosidic Phosphatases: phosphoester Nucleases: phosphoester
6 Classification and Names of Enzymes:
Add or remove groups involving a double bond without hydrolysis
-No oxidation or hydrolysis
Lyase
Decarboxylases: carboxyl
Deaminases: amino
Dehydratases: removes H2O
Hydratases: add H2O
6 Classification and Names of Enzymes:
Rearranging atoms in a molecule to form an isomer
-Changes position; ex: Glucose 1–> glucose 6
-Rearrangement or confirmation of the atoms in a molecule
Isomerase
Isomerases
Epimerases
Racemases
Mutases
6 Classification and Names of Enzymes:
Form bonds between molecules using ATP energy
Used when required simultaneous input of energy, when high energy is needed in the reaction
Ligase
Synthetases
Carboxylases
Models of Enzyme Action:
Small part of an enzyme’s structure that is actually involved in catalysis/ reaction
Three – dimensional entity formed by groups that come from different parts of the protein chains
Formed due to folding and bending of proteins
Enzyme Active Site
Place where substrate binds to an enzymes
Crevice-like; small opening = active site
Has different shapes, geometrically: basis on what substrate can react to the enzyme
There are some enzymes that have more than 1 active sites
Models of Enzyme Action:
The intermediate reaction species that is formed when a substrate binds to the active site of an enzyme.
Needed for the activity of an enzyme
Enzyme-Substrate Complex
Orientation and proximity is favorable and making the reaction fast
When substrate bind to enzyme it will form a product, it will then be released and then it will turn back as an enzyme and can be used again
2 Models of Enzyme-Substrate Complex:
Active site in the enzyme has the fixed, predetermined, rigid geometrical conformation.
Active site shape cannot be changed, doesn’t adjust its shape
Lock and Key Model
Substrates with a complementary geometry of enzymes can be accommodated.
Only substrate of a specific shape and chemical nature can bind to the active site
The substrate and enzyme active site have complementary shapes and chemical nature
2 Models of Enzyme-Substrate Complex:
Enzyme’s active site is not rigid and static, is the one to adjust to the shape
There’s a constant change in shape
Allows for changes in the shape or geometry of the active site of an enzyme to accommodate a substrate.
Induced- Fit Model
Active site shape changes, as long as it can accommodate the substrate
Result of the enzyme’s flexibility; it adapts the incoming substrate.
Substrate contact with the enzyme will change the shape of the active site
4 Enzyme Specificity:
One type of reaction for one substrate
Urease: Urea
Catalase: H2O2
Absolute
restrictive not common
4 Enzyme Specificity: One type of reaction for substrate with the same functional groups -involves structurally similar compounds Hexokinase: CHO; hexose (glucose) Carboxypeptidase: proteins; carboxyl
Group
4 Enzyme Specificity:
One type of reaction for a particular chemical bond
-respective of the structural features in the vicinity of the bonds
Lipase: ester bond
Phosphatase: phosphate ester
Linkage
general, common
4 Enzyme Specificity:
One type of reaction for a particular stereoisomer
-Chirality is involved (D or L)
-Enzyme that can distinguish between stereoisomers
Isomerase
Stereochemical
changes the arrangement to form another substrate
Factors Influencing Enzyme Activity:
↑ Enzyme + ↔️Substrate (constant) = ↑ Enzyme Activity
↔️E (constant) + ↑S = SATURATION CURVE
Already reached the maximum rate; there will be a plateau, no increase in enzyme reaction for it has reached the maximum
The greater enzyme concentration, greater enzyme activity
Enzyme and substrate concentration
Factors Influencing Enzyme Activity:
Changes the conformation of the enzymes
Can denature enzyme due to high temperature
Higher temperature, higher kinetic energy = decrease enzyme activity; denaturing of enzyme
Temperature
Until optimum temperature is not reached, as long as the higher the temperature = higher kinetic energy = increase in number of reactant collisions = increase enzyme activity
Human enzymes: 37 deg. Celsius (normal body tempt)
Increase body temperature (high fever) = decrease enzyme activity = fatal
temperature at which the rate of the enzyme catalyze reaction is maximum
Optimum temperature
Usually 37 degrees C
Factors Influencing Enzyme Activity:
R groups of amino acids have proposer charge
Variation of pH can affect the ions of groups on the substrate
Drastic change in pH: affects the enzyme activity = denature enzyme = no activity
Except for pepsin (2.0, stomach) and trypsin (8.0, small intestine): digestive enzymes
pH
pH at which the enzyme has maximum activity
Optimum pH
7.0-7.5
Human: 7.0-7.5
Blood pH: 7.35 - 7.45
Factors Influencing Enzyme Activity:
At a constant enzyme concentration, the enzyme activity increases with increase substrate concentration
But it could reach a saturation curve: concentration has reached maximum rate; all active sites of enzymes are full
Substrate concentration
No matter how many substrate is present, enzyme activity will not increase unless more enzymes are added to increase activity
Factors Influencing Enzyme Activity:
Enzymes are not consumed in the reactions but rather hastens the reaction
Greater the enzyme concentration = greater the reaction rate
At a constant substrate concentration the enzyme activity increases as long as enzyme concentration increases as well
Enzyme concentration
substrate concentration
Number of substrate molecules transformed per minute by one molecule of enzyme under optimum conditions of temperature, pH and saturation of the substrate.
Turnover number
Ex: Catalase: 5,600,000, Lactate dehydrogenase: 60,000, DNA Polymerase I: 900
Enzyme Inhibition:
Slows or stops the normal catalytic activity of the enzyme; binds to enzyme
Change the protein structure of an enzyme
May be competitive or noncompetitive
Some effects are irreversible
Inhibitors
Has a structure and charge similar to substrate
Occupies active site
Competes with substrate for same active site
Competitive Inhibition
Has effect reversed by increasing substrate concentration
As long as substrates are added, it can ‘steal’ the active site from others
Does not have a structure like substrate
Binds to the enzyme but not active site, but on the allosteric site
Changes the shape of enzyme and active site
Noncompetitive Inhibition
Substrate cannot fit altered active site = No reaction occurs; prevents enzyme activity
Effect is not reversed by adding substrate
Ex: heavy metals: Pb, Ag, Hg
Inactivates enzymes by forming a strong covalent bond to an amino acid side-chain group at the enzyme’s active site
Enzyme is inactivated when binded to active site; permanently inactivate enzyme
Irreversible Inhibitor
Does not reverse the inhibition process
Enzyme is permanently deactivated
Effect is not reversed by adding substrate
Ex: chemical warfare agents: nerve gases, insecticides (organophosphate)
Feedback Regulation:
Pathway is inhibited by accumulation of final product
Negative Feedback
Feedback Regulation:
Regulatory molecule stimulates the activity of the enzyme, usually between 2 pathways
↑ ADP levels cause the activation of the glycolysis pathway to make more ATP
Positive feedback
ODD MAN OUT:
Medical Uses of Enzymes
1. Ensures that our skin is hydrated, moisturized, and nourished
2. Used to diagnose certain diseases: SGOT, SGPT, LDH, Amylase, Lipase (marker for pancreas)
3. Appearance of these enzymes in the blood often indicates that there is tissue damage in an organ and that cellular contents are spilling out into the bloodstream.
4. Used in the treatment of disease: some antibiotics that have enzymes
- Ensures that our skin is hydrated, moisturized, and nourished
